--- a/src/ccache.cpp
+++ b/src/ccache.cpp
@@ -1815,6 +1815,7 @@ get_manifest_key(Context& ctx, Hash& has
                            "CPLUS_INCLUDE_PATH",
                            "OBJC_INCLUDE_PATH",
                            "OBJCPLUS_INCLUDE_PATH", // clang
+                           "GCC_HONOUR_COPTS",
                            nullptr};
   for (const char** p = envvars; *p; ++p) {
     const char* v = getenv(*p);
